U.S. Pat. No. 4,422,040 to Raider et al, which is incorporated by reference herein, discloses a method of quickly testing a stepping motor. The aforesaid Raider et al patent provides a satisfactory test method but requires a mechanical connection to the rotor shaft and uses relatively powerful currents.
The method of the aforesaid Raider et al patent is not capable of automatically detecting sources of internal drag such as interference between the rotor and stator of the stepping motor or high roller bearing friction. The roller bearings rotatably support opposite ends of the rotor shaft in the stator.
One means for testing a stepping motor for excessive friction has been to manually rotate the rotor shaft and have a person determine, by hand feel feedback, as to whether there is excessive friction. This is not satisfactory since the person may either pass defective motors or reject too many acceptable motors since the determination is dependent upon the subjective feel in the person's hand.
This manual testing also requires a relatively long period of time. The manual testing also must be accomplished at a different time than when there is testing of the motor for shorts such as in the aforesaid Raider et al patent, for example. Thus, manual testing for excessive friction not only lacks uniformity but also increases the time and cost of testing.
While the method of the aforesaid Raider et al patent satisfactorily performs tests of most of the important performance parameters of a stepping motor, it cannot reliably detect phase-to-phase and phase-to-ground short circuits. Therefore, in addition to not being able to automatically test a stepping motor for excessive friction, the method of the aforesaid Raider et al patent also cannot recognize certain short circuits.